The 1972 screenprint from Hopper's art collection is done in hues of mostly blues and greens, including a deep blue face for Mao, the founder of the modern communist state.
It had been had been estimated to sell for $20,000 to $30,000 at the two-day auction of hundreds of works from the actor's collection and personal memorabilia from his California home.
Mao was among Warhol's iconic subjects. Hopper's painting was unique because it included bullet holes fired after the notoriously wild actor got spooked and "mistook the portrait on his wall for Mao himself and shot at it," according to Christie's.
Hopper, who died of cancer last year aged 74, later showed Warhol the bullet holes, and the pair agreed to consider the work a collaboration. Warhol drew circles around the holes, labelling the one over Mao's right shoulder "warning shot" and the one at his upper left eyelid "bullet hole."
Much of Hopper's most valuable art was sold in November during Christie's contemporary and post-war auction, raising more than $10 million for his estate.
The sale, which also included works by Annie Leibovitz, Marcel Duchamp, Helmut Newton as well as more Warhols, wraps up on Wednesday.